Wolfgang von Schwarzenfeld's sculptures in a Berlin park were meant to promote world peace, but the 79-year-old German now finds himself at war with a Venezuelan tribe which accuses him of stealing a sacred pink stone known to them as "Grandmother".

The Venezuelan government is championing the Pemon Indians of the "Gran Sabana" region by demanding the return of the polished stone from Berlin's Tiergarten park - putting the German government in something of a dilemma.

With Caracas calling it robbery, and the sculptor arguing that the stone was a legal gift, the monolith is emitting more negative energy than its esoteric fans in Berlin are used to. Blissfully unaware of the diplomatic tug-of-war, Robert, a Berlin gardener, got off his bicycle to light joss sticks among the stones from five continents that form the "Global Stone Project", awaiting friends for an afternoon shamanic ritual.

But newly arrived Venezuelan tourists Grecia Melendez and Juan Carlos Brozoski knew all about the war of the stone and suspected there were political motives behind the protests. "(President Hugo) Chavez always wants a conflict with someone," said 32-year-old Melendez, taking photos of the 12 cubic meter stone, which is engraved with the word "love" in different languages - and graffiti with couples' names and hearts.

Von Schwarzenfeld, a frail figure with whispy white hair and scuffed brown shoes, waved a sheaf of documents authorizing the removal of the stone from the Canaima National Park in 1998. As with all the stones arranged in a circle in Berlin, a "sister" stone remained behind. Every summer solstice, their burnished surfaces reflect the sun "as a symbol of a united mankind, hopefully one day in peace", he said.

The project was inaugurated in 1999 near Berlin's landmark Potsdamer Platz and Brandenburg Gate. As children played among the stones, Von Schwarzenfeld defied Venezuela to take back what he called a "gift to Berlin" from former president Rafael Caldera. "Peace for me does not mean the absence of conflict," said the artist, undeterred by threats and what he too suspects are "political motivations" behind the tussle over the stone.

ALL THE ANTS YOU CAN EAT

A video circulated on Youtube has mobilized public opinion in Venezuela, recounting the mythical origins of the Kueka (grandmother in the Pemon language) and its pair, and voicing locals' sense of loss. "This man decided to take the Kueka without caring about its cultural value for the Pemon community," Venezuelan activist and ecologist Any Alarcon says in the video.

Culture Minister Pedro Calzadilla told state television the donation was "illegitimate" because the stone was part of "the cultural patrimony of the (Pemon) community". Prosecutors are looking into the stone's removal because "whoever authorized the removal of the Grandmother committed a crime", he said.

After Pemon tribespeople demonstrated outside Germany's embassy last week with spears, feather headdresses and banners saying "The Pemon People Want Our Wise Grandmother Back", the German envoy promised to relay their feelings to Berlin, while telling them it would be no easy task to return the stone.

German Foreign ministry spokesman Andreas Peschke said Berlin wanted a solution "agreed by all sides - Venezuela, the indigenous groups, the artist and the city of Berlin". Von Schwarzenfeld was not convinced, saying the stone's removal would sacrifice "the 15 years of my life and all the money I spent. If it is taken away, it ruins the whole project."

Beside him stood German anthropologist Bruno Illius, who has studied the Pemon tribe for two decades. He said there was "no such thing as a 'holy stone' for the Pemones, just small magical stones with practical purposes, like helping you to catch fish".

Illius rubbished stories about the stone's removal bringing misfortune on the tribe, like drought and the disappearance of the ants they eat in spicy sauce, saying he had eaten plenty of ants on three visits to the region, as recently as last year. "This is all a fraud, a deception," the professor said.